1. Technical Field
The invention relates to image processing. More particularly, the invention relates to image classification and halftone detection, especially with regard to digitized documents, acquired for example by digital scanning, and the reproduction of such images on digital color printers.
2. Description of the Prior Art
Electronic documents contain a variety of information types in various formats. A typical page of such document might contain both text (i.e. textual information) and images (i.e. image information). These various types of information are displayed and reproduced in accordance with a particular formatting scheme, where such formatting scheme provides a particular appearance and resolution as is appropriate for such information and printing device. For example, text may be reproduced from a resident font set and images may be reproduced as continuous tone (contone) or halftone representations. In cases where a halftone is used, information about the specific screen and its characteristics (such lines per inch (Ipi)) is also important.
It is desirable to process each type of information in the most appropriate manner, both in terms of processing efficiency and in terms of reproduction resolution. It is therefore useful to be able to identify the various information formats within each page of a document. For example, it is desirable to identify halftone portions of a document and, as appropriate, descreen the halftone information to provide a more aesthetically pleasing rendition of, e.g an image represented by such information.
In this regard, various schemes are known for performing halftone detection. See, for example, T. Hironori, False Halftone Picture Processing Device, Japanese Publication No. JP 60076857 (1 May 1985); I. Yoshinori, I. Hiroyuki, K. Mitsuru, H. Masayoshi, H. Toshio, U. Yoshiko, Picture Processor, Japanese Publication No. JP 2295358 (Dec. 6, 1990); M. Hiroshi, Method and Device For Examining Mask, Japanese Publication No. JP 8137092 (May 31, 1996); T. Mitsugi, Image Processor, Japanese Publication No. JP 5153393 (Jun. 18, 1993); J.-N. Shiau, B. Farrell, Improved Automatic Image Segmentation, European Patent Application No. 521662 (Jan. 7, 1993); H. Ibaraki, M. Kobayashi, H. Ochi, Halftone Picture Processing Apparatus, European Patent No. 187724 (Sep. 30, 1992); Y. Sakano, Image Area Discriminating Device, European Patent Application NO. 291000 (Nov. 17, 1988); J.-N. Shiau, Automatic Image Segmentation For Color Documents, European Patent Application No. 621725 (Oct. 26, 1994); D. Robinson, Apparatus and Method For Segmenting An Input Image In One of A Plurality of Modes, U.S. Pat. No. 5,339,172 (Aug. 16, 1994); T. Fujisawa, T. Satoh, Digital Image Processing Apparatus For Processing A Variety of Types of Input Image Data, U.S. Pat. No. 5,410,619 (Apr. 25, 1995); R. Kowalski, D. Bloomberg, High Speed Halftone Detection Technique, U.S. Pat. No. 5,193,122 (Mar. 9, 1993); K. Yamada, Image Processing Apparatus For Estimating Halftone Images From Bilevel and Pseudo Halftone Images, U.S. Pat. No. 5,271,095 (Dec. 14, 1993); S. Fox, F. Yeskel, Universal Thresholder/Discriminator, U.S. Pat. No. 4,554,593 (Nov. 19, 1985); H. Ibaraki, M. Kobayashi, H. Ochi, Halftone Picture Processing Apparatus, U.S. Pat. No. 4,722,008 (Jan. 26, 1988); J. Stoffel, Automatic Multimode Continuous Halftone Line Copy Reproduction, U.S. Pat. No. 4,194,221 (Mar. 18, 1980); T. Semasa, Image Processing Apparatus and Method For Multi-Level Image Signal, U.S. Pat. No. 5,361,142 (Nov. 1, 1994); J.-N. Shiau, Automatic Image Segmentation For Color Documents, U.S. Pat. No. 5,341,226 (Aug. 23, 1994); R. Hsieh, Halftone Detection and Delineation, U.S. Pat. No. 4,403,257 (Sep. 6, 1983); J.-N. Shiau, B. Farrell,Automatic Image Segmentation Using Local Area Maximum and Minimum Image Signals, U.S. Pat. No. 5,293,430 (Mar. 8, 1994); and T. Semasa, Image Processing Apparatus and Method For Multi-Level Image Signal, U. S. U.S. Pat. No. 5,291,309 (Mar. 1, 1994).
While there is a substantial volume of art that addresses various issues associated with halftone generation and detection, there has not heretofore been available a fast and efficient technique for effective image classification and for detection of halftone segments and other components of a document. In particular, such techniques as are known do not effectively detect halftone information and classify image regions, especially with regard to efficient algorithms based upon such factors as boundary sets for image information within a single image plane and cross color differences for image information across multiple images planes.
It would be advantageous to provide an improved technique for image classification and halftone detection.
It would also be advantageous to provide a technique that has the to detect halftone components of a document without having predetermined information about the halftone technique used to produce the original image, and moreover, without having detailed information on the specific characteristics of that halftone technique, such as the type of screen used, the threshold array, or the Ipi.